Genetic, biochemical and biophysical methods are being used to examine a) the roles of bacterial and phage recombination systems in bacteriophage lambda recombination; b) the impact of DNA sequence non-homologies on recombination; c) the processing of base pair mismatches and DNA sequence non-homologies in artificially constructed heteroduplex molecules of lambda DNA; d) the role of recombination in post-replication repair, and e) the mechanism of Mu DNA integration following lytic infection.